Apparatus responsive to the amount of refrigerant flow in a refrigerant flow in a refrigerant circulating system

ABSTRACT

An apparatus responsive to the amount of refrigerant flow in a refrigerant circulating system includes a sensing capacitor mounted in a refrigerant passage, the capacitance of the sensing capacitor being varied depending on a change in the dielectric constant of the refrigerant which in turn being dependent on the amount of the refrigerant. The sensing capacitor forms an element of a resistance-capacitance oscillatory circuit and it also forms a ring oscillator together with another capacitor and a plurality of inverters and resistors. The oscillation frequency of the ring oscillator is detected to determine the amount of the refrigerant flowing through the refrigerant passage.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus responsive to the amountof refrigerant flow in a refrigerant circulating system forrefrigerating purposes, for example, which is designed for use in airconditioners such as automobile coolers.

Refrigerant circulating systems which have heretofore been used forrefrigerating purposes are usually of the type in which a compressor, acondenser, a pressure regulator and an evaporator are interconnected bya refrigerant pipeline and a refrigerant is sealed in the system. Foruse with this type of systems several methods have been proposed for thepurpose of detecting the amount of refrigerant flow to prevent adecrease in the cooling capacity of the refrigerator or damage to therefrigerator due to the leakage of the refrigerant. These known methodsinclude the use of refrigerant flow detecting apparatus designed toelectrically detect a change in the dielectric constant in therefrigerant passage, for example, disclosed in Japanese Laid-OpenPublication No. 16743/77.

However, these known refrigerant flow detecting apparatus of thedielectric constant responsive type are disadvantageous in that a changein the dielectric constant is small as compared with a change in theamount of refrigerant flow and this requires an increase in the size ofa dielectric constant sensor, an increase in the amplification factorand accuracy of the electric circuit and the like, thus requiring anincrease in the size and complexity of the apparatus or the use ofexpensive components.

SUMMARY OF THE INVENTION

It is the object of this invention to provide a refrigerant deficiencydetecting apparatus which overcomes the foregoing deficiencies in theprior art, is small in size, has a high degree of accuracy in operationand is practical.

The main feature of this invention may be briefly summarized as follows.When the refrigerant used in a refrigerant circulating system is in gasform, its dielectric constant ε differs from that when it is in liquidform. In the case of Freon-12 (F-12), for example, εg≈1.0 when itchanges to a gas and ε_(l) ≈2.0 when it changes to a liquid. If therefrigerant is in the form of a gas-liquid mixture, its dielectricconstant varies in dependence on the gas-liquid ratio. In accordancewith this invention, to sense the dielectric constant of a refrigerant,a sensing capacitor comprising a pair of electrodes is disposed in arefrigerant passage and a special resistance-capacitance oscillatorcircuit designed to use the sensing capacitor as a displacementcapacitor is connected to it. The resistance-capacitance oscillatorcircuit comprises a plurality of inverters, resistors and capacitors andits oscillation frequency varies considerably with small changes in thecapacitance of the sensing capacitor. The amount of refrigerant flow isindicated to the outside by a display, an indicator or any other outputdevice which is responsive to the oscillation-frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the overall construction of anembodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing the mechanicalconstruction of the refrigerant flow sensor shown in FIG. 1.

FIG. 3 is a longitudinal sectional view showing in detail theconstruction of the sensing capacitor shown in FIG. 2.

FIG. 4 is a wiring diagram showing the circuit construction of therefrigerant flow sensor and the detection signal processing circuitshown in FIG. 1.

FIG. 5 is a timing diagram of the signal voltages which are useful forexplaining the operation of the circuits shown in FIG. 4.

FIG. 6 is a graph showing a relation between the refrigerant flow M andthe intermediate generated voltage V_(e) for explaining the operatingcharacteristics of the electric circuits shown in FIG. 4.

FIG. 7 is a perspective view showing another form of the sensingcapacitor of the refrigerant flow sensor.

FIGS. 8 and 9 are wiring diagrams showing another forms of theresistance-capacitance oscillator circuit connected to the sensingcapacitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in greater detail withreference to the illustrated embodiments.

Referring to FIG. 1, there is illustrated a schematic diagram showingthe overall construction of an embodiment of this invention which isapplied to a cooling refrigerant circulating system of an automobile airconditioner. In the Figure, numeral 1 designates a compressor forforcedly circulating the refrigerant in a pipeline 2 in the directionsshown by arrows, and the compressor 1 is driven by a vehicle engine (notshown) via an electromagnetic clutch 3. Numeral 4 designates a condenserso designed that the refrigerant flowing therethrough is cooled by acooling fan 5 which is operated by the engine or an electric motor.Numeral 6 designates a receiver, and 7 a temperature responsiveexpansion valve. Numeral 8 designates an evaporator disposed in an airconditioner duct (not shown) so that the air supplied from an electricblower 9 is cooled and supplied into the vehicle compartment. Theseunits 1 to 9 provide a known refrigerant cycle.

Numeral 10 designates a temperature sensitive element (e.g., athermistor) for sensing the temperature of the air blown from theevaporator 8, which is connected to a known type of defrosting circuit11 so that when the temperature of the blown air sensed by thetemperature sensitive element 10 is lower than a predetermined value,the defrosting circuit 11 opens an output-stage relay 11a so as to cutoff the supply of power to the electromagnetic clutch 3 from a powersupply battery 12 (supply voltage +V_(B)) and the compressor 1 isstopped. Numeral 13 designates a key switch of the vehicle, such as, anignition switch, and 14 an air conditioner actuating switch. When theswitches 13 and 14 are closed, the power is supplied to the entireapparatus including the electromagnetic clutch 3 and the defrostingcircuit 11 as well as a detection signal processing circuit 15 whichwill be described later.

The detection signal processing circuit 15 and a refrigerant flow sensor16 form a principal part of this invention such that when the detectionsignal applied from the sensor 16 is indicative of deficiency of therefrigerant, a relay 17 is operated and its contacts are opened todisable the operation of the compressor 1. The processing circuit 15further turns on a light-emitting diode 18a of an indicator 18 andthereby alerting the driver to the low refrigerant.

FIGS. 2 and 3 show in detail the construction of the refrigerant flowsensor 16. In FIG. 2, a sensing capacitor 16a comprising a pair ofelectrodes is mounted in a mounting block 19 which is made of a metallicmaterial such as brass and joined with mounting pipes 20a and 20b bysoldering or the like, and the block 19 is connected to a part of thepipeline 2 by a known type of joint 2a. The metallic block 19 is formedwith an opening 19a through which the sensing capacitor 16a is inserted,and fixedly mounted above the opening 19a with an O-ring 22 is a holder21 which is made of brass or the like and adapted to mechanicallysupport the sensing capacitor 16a and contain the electric circuitstherein. The two electrodes of the sensing capacitor 16a are connectedto hermetically sealed electrodes 16b and 16c which are in turn closelyfitted in the holes formed in the holder 21 such that each of theelectrodes 16b and 16c is electrically connected to and supports thesensing capacitor 16a at its one end and the other ends are alsoconnected electrically to associated one of the circuits on an electriccircuit mounting printed circuit board 23 which is fixedly mountedwithin the holder 21. Numeral 24 designates a cover placed to enclosethe upper open end of the holder 21.

As shown in FIG. 3, the sensing capacitor 16a is firmly fitted on theelectrodes 16b and 16c in such a manner that a plurality of disk-shapedelectrically insulating bases 16d (made for example of phenolic resinmaterial) are arranged in layers to form a small gap therebetween, andthe electrodes 16b and 16c are alternately soldered (at 16f) to films16e of conductive material such as copper foils applied to the surfacesof the insulating bases 16d except where the electrodes 16b and 16cpasses as shown in the Figure. Thus a plurality of small capacitancesare provided between the conductive films facing each other through airgaps. These capacitances are connected in parallel by means of theelectrodes 16b and 16c. A composite capacitance of these parallelcapacitances is sensed via the electrodes 16b and 16c. This constructionhas the advantage of increasing the capacitance value of the sensingcapacitor 16a and also making the density of the refrigerant atmosphereflowing in the pipeline 2 uniform at the sensing section.

The electric connections of the refrigerant flow sensor 16 and thedetection signal processing circuit 15 are shown in FIG. 4. In theFigure, numeral 25 designates an oscillation activation circuitcomprising the sensing capacitor 16a (C_(s)) of the refrigerant flowsensor 16 and the electrical elements mounted on the printed circuitboard 23 within the holder 21. In the oscillation activation circuit 25,symbols G₁, G₂, G₃ and G₄ designate inverters each comprising acomplementary metal oxide semiconductor or C-MOS integrated circuit andincluding a supply-side P-channel transistor and a ground-side N-channeltransistor, R₁ and R₂ resistors, and C_(o) and C_(s) first and secondcapacitors of which the second capacitor is the sensing capacitor 16a inthis embodiment. A closed circuit is formed by the first inverter G, theresistor R₁ and the resistor R₂ with which is connected in parallel aseries circuit comprising the second inverter G₂ and the first capacitorC_(o) and a series circuit comprising the third inverter G₃ and thesecond capacitor C_(s) or the sensing capacitor is connected in parallelwith the first capacitor C_(o), thus forming a resistance-capacitancetype oscillator circuit. Symbol Q₁ designates a transistor, R₃, R₄ andR₅ resistors, and C₁ a capacitor. These elements form a waveformreshaping circuit.

The oscillation frequency of this oscillator circuit varies successivelywith variations in the capacitance value (C_(s) ') of the secondcapacitor C_(s). When the refrigerant in liquid form passes the sensingcapacitor 16a, its dielectric constant ε_(l) is about 2.0 so that thecapacitance value increases and the oscillation frequency is increased.On the contrary, when the refrigerant in gas form passes, the dielectricconstant becomes about 1.0 so that the capacitance value decreases andthe oscillation frequency decreases. When the refrigerant is a mixtureof liquid and gas, its dielectric constant ε (l, g) assumes a valuewhich is intermediary between 1.0 and 2.0 and the oscillation frequencyis determined correspondingly.

The function of the resistance-capacitance oscillator circuit will bedescribed in detail in connection with the description of the operationof the apparatus which will be described later.

In the detection signal processing circuit 15 shown in FIG. 4, numeral26 designates a known type of frequency-to-voltage conversion circuitwhich generates at its output terminal a DC voltage corresponding to theoscillation frequency from the oscillation activation circuit 25.Numerals 27 and 28 designate comparators for comparing the DC voltagewith reference voltages V_(f) and V_(g) which are determined by voltagedividing resistors 29, 30 and 31. The comparison reference voltage V_(f)of the first comparator 27 which controls the indicator 18, is selectedhigher than that V_(g) of the second comparator 28 which controls therelay 17. Numeral 32 designates a transistor which is controlled by thesecond comparator 28 to operate the relay 17.

With the construction described above, the operation of the embodimentwill now be described. Firstly, when the amount of refrigerant flow issufficient in the refrigerant circulating system shown in FIG. 1, therefrigerant flowing through between the electrodes of the sensingcapacitor 16a of the refrigerant flow sensor 16 is in liquid form sothat its dielectric constant ε_(l) is about 2.0 and thus the variablecapacitance C_(s) ' of the second capacitor C_(s) shown in FIG. 4increases or becomes C_(s) '=ε_(l) ×C_(s). In this condition, theresistance-capacitance oscillator circuit operates as follows. Namely,if the capacitance value C_(s) ' of the second capacitor C_(s) isgreater than the constant capacitance value C_(o) ' of the firstcapacitor C_(o), the circuit operates in the similar manner as theordinary ring oscillator. Thus, when the output level of the inverter G₃changes from "0" to "1," the voltage level at a point a momentarily goesnear to "1," thus causing the output voltage of the inverter G₁ tochange from "1" to "0," the output voltage of the inverter G₂ from "0"to "1" and the output voltage of the inverter G₃ from "1" to "0." Whenthis occurs, the voltage level at the point a momentarily goes near to"0" and the inverters G₁, G₂ and G₃ are again caused to change theirstates. This on-off operation is repeated to produce oscillations andthe oscillation period approaches a short value which is determined bythe transmission time lag of the inverters. In other words, theoscillation frequency is high. In this case, the DC voltage V_(e)appearing at the output terminal of the frequency-to-voltage conversioncircuit 26 becomes higher than the reference voltages V_(f) and V_(g) ofthe first and second comparators 27 and 28 and the output levels of thecomparators 27 and 28 go to "0. " As a result, the indicator 18 is notturned on and the relay 17 is not energized holding its normally closedcontacts in the closed position. Thus, the defrosting circuit 11controls the energization and deenergization of the compressor drivingelectromagnetic clutch 3.

When the flow of the refrigerant in the refrigerant circulating systemdecreases due to the leakage, the liquid refrigerant passing the sensingcapacitor 16a decreases so that the capacitance C_(s) ' of the secondcapacitor C_(s) shown in FIG. 4 becomes C_(s) '=ε(l, g)×C_(s) and thisis smaller than that obtained when the refrigerant is entirely in liquidform. This decrease is proportional to a decrease in the amount of theliquid refrigerant. The capacitance value C_(o) ' of the first capacitorC_(o) is selected equal to that capacitance value of the secondcapacitor C_(s) which corresponds to a certain decrease in the liquidrefrigerant.

Thus, when a relation C_(s) '>C_(o) ' occurs between the two capacitancevalues, the resistance-capacitance oscillator circuit operates asindicated by the waveforms shown in FIG. 5 and its oscillation frequencydecreases with a decrease in the value of C_(s) '. Assuming that at thetime t=T_(o) the output voltage V_(c) of the second inverter G₂ goes tothe "1" level (see FIG. 5) and the output voltage V_(d) of the thirdinverter G₃ goes to the "0" level, the first and second capacitors arebiased in the opposite directions by the input and output voltages ofthe third inverter G₃. As a result, the voltage V_(a) of the firstcapacitor C_(o) is cancelled partially by the voltage of the secondcapacitor C_(s) to a value V_(o) which is lower than the sum of a DCvoltage V_(cc) and an inverter threshold voltage V_(TH). Thus, thedifferential current flows via the closed circuit formed by the firstcapacitor C.sub. o, the resistor R₂, the ground-side N-channel of theinverter G₁, the DC power supply and the supply-side P-channel of theinverter G₂ and the closed circuit formed by the first and secondcapacitors C_(o) and C_(s), the ground-side N-channel of the thirdinverter G₃, the DC power supply and the supply-side P-channel of thesecond inverter G₂, and the voltage V_(a) across the first capacitorC_(o) decreases gradually along with the passage of the time t. In thiscase, the output voltage of the second inverter G₂ remains at the "1"level.

When the time t reaches T₁, the voltage V_(a) drops to the thresholdvoltage V_(TH) so that the output voltage V_(b) of the first inverter G₁goes to the "0" level, the output voltage V_(c) of the second inverterG₂ to the "1" level and the output voltage V_(d) of the third inverterG₃ to the "0" level. As a result, as mentioned previously, the voltageV_(a) of the first capacitor C_(o) is cancelled partially by the voltageof the second capacitor C_(s) and it changes from the voltage V_(TH) toa value V₁ which is higher than -V_(TH). Thus, the differential currentflows through the closed circuit formed by the DC power supply, thesupply-side P-channel of the first inverter G₁, the resistor R₂, thefirst capacitor C_(o) and the ground-side N-channel of the secondinverter G₂ and the closed circuit formed by the DC power supply, thesupply-side P-channel of the third inverter C₃, the second and firstcapacitors C_(s) and C_(o) and the ground-side N-channel of the secondinverter G₂, and the voltage V_(a) across the first capacitor C_(o)increases gradually with the passage of the time t. In this case, theoutput voltage of the second inverter G₂ remains at the "0" level.

When the time t reaches T₂, the voltage V_(a) rises to the thresholdvalue V_(TH) so that the output voltage V_(b) of the first inverter G₁goes to the "1" level, the output voltage V_(c) of the second inverterG₂ to the "0" level and the output voltage V_(d) of the third inverterG₃ to the "1" level. When this occurs, the voltage V_(a) across thefirst capacitor C_(o) changes to a value V_(o) which is lower than(V_(CC) +V_(TH)) in the same manner as mentioned previously. Thereafter,this process is repeated and thus the oscillation activation circuitproduces oscillations at a period (T₂ -T_(o)). Since the magnitude ofthe voltage V_(a) varies in dependence on the magnitude of thecapacitance value C_(s) ' of the second capacitor C_(s), the oscillationfrequency varies so that the DC voltage V_(e) produced by thefrequency-to-voltage conversion of the frequency-to-voltage conversioncircuit 26 is varied in accordance with such characteristic as shown inFIG. 6 with respect to the amount of the refrigerant sealed in therefrigerant circulating system.

Thus, when the amount of refrigerant flow reaches a value M₁ which issmaller than the normal sealed amount M_(o) by a predetermined value,the DC voltage V_(e) becomes lower than the reference voltage V_(f) andthe output voltage of the first comparator 27 changes to the "1" level.As a result, the indicator 18 is now energized and it turns on. When therefrigerant flow decreases further to the value of M₂, the DC voltageV_(e) becomes lower than the reference voltage V_(g) and the outputvoltage of the second comparator 28 also changes to the "1" level. As aresult, the transistor 32 is turned on and the relay 17 is energizedthus opening its normally-closed contacts. When this occurs, theelectromagnetic clutch 3 is deenergized so that the compressor 1 isstopped and the operation of the refrigerant circulating system isstopped. Thus, by effecting the indication and the stoppage of therefrigerant circulating system operation at the two different stages, itis possible to give an early warning for replenishment of refrigerant bythe indication at the first stage and to protect the refrigerantcirculating system from damage by its forced stoppage at the secondstage.

It should be noted that the desired effect can be produced by only oneor the other of the indication and the stoppage of the system operationif occasion demands.

The objective of this invention can also be accomplished by thefollowing modifications. For example, a sensing capacitor 16a' shown inFIG. 7 may be disposed in the refrigerant passage of the refrigerantcirculating system. In the Figure, numerals 16b' and 16c' designatehermetically sealed electrodes of the same type shown in FIG. 2, and16d' and 16e' cylindrical metal electrodes. A capacitance is providedbetween the inner side of the outer electrode 16d' and the outer side ofthe inner electrode 16e', and an electric connection is made between theelectrode 16b' and the inner electrode 16e' and between the electrode16c' and the outer electrode 16d'. In this case, a part of therefrigerant pipeline may be used as the outer electrode. Also, where astratified electrode structure is used as shown in FIGS. 2 and 3, theelectrodes may be formed into any other shape than the disk shape.

While, in the oscillation activation circuit 25, the second capacitorC_(s) is used as the sensing capacitor, it is possible to use the firstcapacitor C_(o) as the sensing capacitor and to reverse the inputpolarities of the comparators 27 and 28 and reverse the magnitudes oftheir reference voltages so as to cause the comparators to successivelydetect the oscillation frequency increasing with decrease in the amountof refrigerant flow.

While, in the above-described embodiment, the oscillation circuitincludes the single inverter G₃ connected between the terminal c of thecapacitor C_(o) and the terminal d of the capacitor C_(s), the inverterG₃ may be replaced with an odd number of inverters G₃ to G_(n) as shownin FIG. 8 to obtain the same functional effect as in the case of thepreviously described embodiment.

FIG. 9 shows a modification of the above-described embodiment, in whicha closed circuit is formed by the first capacitor C_(o), the resistor R₁and the inverter G₁, a series circuit of the resistor R₂ and theinverter G₂ is connected in parallel with the first capacitor C_(o), aseries circuit of the inverter G₃ and the resistor R'₂ is connected inparallel with the resistor R₂ and a series circuit of an inverter G_(3')and the second capacitor C_(s) is connected in parallel with a resistorR_(2'). In accordance with this modification, when the DC voltage V_(CC)is applied from the DC power supply to each of the inverters, thecapacitors C_(o) and C_(s) are biased in the opposite directions by theinput and output voltages of the inverters G₂, G₃ and G_(3') which areodd in number, thus producing essentially the same functional effect asexplained in connection with the above-described embodiment.

Further, each of the inverters may be comprised of a transistor insteadof an integrated circuit.

Further, while, in the above-described embodiment, the detection signalprocessing circuit 15 comprises the frequency-to-voltage conversioncircuit and the voltage comparison circuit, the circuit 15 may becombined with a detecting circuit including a digital or analog countingcircuit for repeatedly counting the number of pulse signals applied in aunit time from the oscillation activation circuit 25 so as to generatean output signal when the count value attains a predetermined value.

Further, in the above described embodiment, the detection signalprocessing circuit 15 may include a plurality of comparators withdifferent reference voltages so as to detect the amount of refrigerantflow at many points and indicate the refrigerant flow at a plurality oflevels, for example.

On the other hand, where the flow of refrigerant remains unstable duringseveral tens of seconds after starting the operation of the refrigerantcirculating system and the refrigerant flow sensor is disposed forexample in a part of the refrigerant pipeline, the refrigerant flowsensor may possibly indicate a value which is different from that of therefrigerant flowing past the refrigerant flow sensor in the stable flowcondition. In such cases, in order to prevent the output unit fromcoming into operation during several tens of seconds after theenergization of the compressor driving electromagnetic clutch 3, a timercircuit may be additionally provided so as to forcibly apply the supplyvoltage V_(cc) to the output terminal of the frequency-to-voltageconversion circuit 26 and thereby to prevent any erroneous indicationand any erroneous stoppage of the refrigerant circulating system.

Still further, while, in the above-described embodiment, the output unitgives an indication and stops the operation of the refrigerantcirculating system in response to decrease in the amount of refrigerantflow, noting the fact that the cooling capacity of the evaporator 8decreases with decrease in the amount of refrigerant flow, in the caseof a ventilating unit including the evaporator 8 of the automobile airconditioner, a heating heat exchanger having an adjustable capacity (aheat exchanger is known which utilizes the cooling water of theautomobile engine as a source of radiant heat and which includes amixture ratio adjusting damper for adjusting the amount of air flowingthrough the bypass of the heat exchanger) may be positioned downstreamof the evaporator 8 in addition to an electric control unit adapted toautomatically control the heating capacity in accordance with thetemperatures inside and outside the vehicle compartment, whereby theadjusting output of the electric control unit is corrected in accordancewith the amount of refrigerant flow.

Still further, instead of stopping the operation of the refrigerantcirculating system, a sounder (e.g., a buzzer) which is capable ofmaking a relatively rich sound may be used.

It will thus be seen from the foregoing that the present invention has agreat advantage that by virtue of the use of a small oscillator circuitwhose oscillation frequency varies successively in accordance with theamount of refrigerant flow, an apparatus is provided which is small insize and responsive with a high degree of accuracy to the amount ofrefrigerant flow, thus ensuring an accurate operation.

We claim:
 1. An apparatus responsive to the amount of flow of arefrigerant in a refrigerant circulating system, said apparatuscomprising:sensing capacitor means including a pair of electrodes anddisposed in a portion of a refrigerant passage of said refrigerantcirculating system; a resistance-capacitance oscillator circuitincluding said sensing capacitor means as a displacement capacitor, saidresistance-capacitance oscillator circuit forming a ring oscillatorincluding a plurality of inverters, a plurality of resistors and firstand second capacitors, said first capacitor forming said sensingcapacitor means and said second capacitor having a predeterminedcapacitance value being biased in opposite directions to each other byinput and output voltages of at least one of said inverters; and outputmeans responsive to oscillation frequencies of saidresistance-capacitance oscillator circuit.
 2. An apparatus according toclaim 1, wherein said resistance-capacitance oscillator circuitcomprises a closed circuit including first one of said inverters and oneof said resistors, a first series circuit including second one of saidinverters and said first capacitor and connected in parallel with saidone resistor, and a second series circuit including third one of saidinverter and said second capacitor and connected in parallel with saidfirst capacitor, wherein either said first capacitor or said secondcapacitor forms said sensing capacitor means, and wherein saidcapacitors are biased in opposite directions to each other by input andoutput voltages of said third inverter when a DC supply voltage isapplied to each of said invertors.
 3. An apparatus according to claim 1,wherein said sensing capacitor means includes a plurality of flat plateelectrodes substantially parallel to said refrigerant passage andarranged in layers.
 4. An apparatus according to claim 1, wherein saidoutput means includes two activation means responsive to the oscillationfrequencies of said resistance-capacitance oscillator circuit andoperable in response to at least two of said oscillation frequencies. 5.An apparatus according to claim 4, wherein said two activation meansinclude indicator means and means for stopping the operation of saidrefrigerant circulating system.